The present invention relates to a measuring instrument that measures the amount of displacement of a movable member relative to a fixed member.
A vernier caliper, a micrometer, an indicator, a test indicator, a height gauge and the like are known as digital measuring instruments that measure the dimensions of an object to be measured. For example, a test indicator described in Japanese Examined Utility Model Registration Application Publication No. 2-45762 is known.
This type of measuring instrument includes a fixed member, a movable member configured to be movable in relation to the fixed member, detecting means for detecting the amount of displacement of the movable member relative to the fixed member, and a display section for displaying the amount of displacement of the movable member relative to the fixed member, which is detected by the detecting means.
As shown in FIG. 9, an effective measurement range β narrower than the movement stroke α of the movable member, namely, the effective measurement range β (range starting at A and ending at B) whose values are larger than the lower limit C and smaller than the upper limit D of the movement stroke α of the movable member undergoes accuracy inspection by the manufacturer, and so accuracy of only measurements within the effective range β are guaranteed.
For this reason, after a measuring instrument is set with respect to an object to be measured, the movable member is caused to move in relation to the object while measurement is made, in order to ensure that measurement is normally made within the effective measurement range β. Alternatively, a reference gauge and the object are respectively measured, thereby determining the difference between the object and the reference gauge, namely, a comparison measurement is performed.
However, a test indicator described in Japanese Examined Utility Model Registration Application Publication No. 2-45762 has a disadvantage in that the starting point A and the ending point B of the effective measurement range β are not definitely defined in relation to the lower limit C and the upper limit D of the movement stroke α of the movable member. For this reason, when measurement is made, the effective measurement range is narrowed to maintain accuracy, thereby preventing measurement uncertainty.
This makes setting work burdensome, which may cause measurements to be carelessly made outside the effective measurement range, leading to degraded measurement reliability.